1. Field of the Invention
The present invention relates to charge warning devices and more particularly to charge warning devices for an AC generator with a contactless type voltage regulator.
2. Prior Art
In the prior art, AC generator for use in motor vehicles have included contact-type regulators which mechanically interrupt the field current of an AC generator by means of a contact thereby making the generated voltage be constant. However, recently, there has been a tendency to provide the AC generator with a contactless type regulator in which the field current is interrupted by a semiconductor consisting mainly of a hybrid IC. This type of AC generator with a contactless type regulator, having no mechanical contacts, has many desirable characteristics such as a higher reliability and a long service life.
Shown in FIG. 1 is one example of a prior art circuit for an AC generator having a contactless type regulator. The AC generator 10 includes three-phase wired stator coil 12, rectifiers 14, a field coil 16 and exciting diodes 18 for supplying current to the field coil 16. Incorporated therein is an IC regulator 20 consisting of a semiconductor circuit using a hybrid IC. A charge warning lamp 22 is provided with one terminal being connected to regulator terminal L of alternator 10. An ignition switch 24 is connected to the other terminal of the charge warning lamp 22 via a fust 30. A battery is connected to battery terminal B of the AC generator 10 and connected to the other terminal of the ignition switch 24 via a fuse 28.
In such a prior art device for indicating the rate of charge in the AC generator, when the ignition switch 24 is off, the charge warning lamp 22 does not light. When the ignition switch 24 is turned on and the engine is in a static condition, the electric potential of the AC generator at point A becomes substantially 0 volts and current supplied from the battery 26 passes through the ignition switch 24, the charge warning lamp 22, the regulator terminal L, field coil 16 and IC regulator 20. As a result, the charge warning lamp 22 lights up. When the engine is started, the AC generator 10 starts to generate electricity and voltage is generated at the point A whereby the opposite ends of the charge warning lamp 22 have substantially the same electrical potential and therefore, the charge warning lamp 22 is out. The charge warning lamp 22 can be checked by turning the ignition switch on and leaving the engine off. If the ignition switch is on and the engine is running and the charge warning lamp 22 is on, electricity is not being generated due to a failure of the AC generator 10. However, with the prior art devices for indicating the rate of charge there has been a certain disadvantage that when the difference in electrical potential between the opposite ends of the charge warning lamp 22 becomes larger than a small amount, even if the AC generator 10 is operating normally, the charge warning lamp 22 turns on to a slight extent whereby the operator may feel uneasy about the function of the AC generator 10.